1. Field of the Invention
The present invention relates to a method for continuously processing an organic solvent-containing air and, more particularly, to a method for processing an organic solvent-containing air comprising carrying out simultaneously and continuously a step of removing organic solvents in air to be processed by adsorbing the organic solvents in an adsorbing member containing an adsorbent such as zeolite supported thereon (adsorbing-removing step), a step of regenerating the adsorbing member which has adsorbed the organic solvents (regenerating step), and a step of burning the organic solvents in the air containing high-concentration organic solvents produced by regenerating the adsorbing member (combustion step).
2. Description of Related Art
Air containing organic solvents such as a halogenated hydrocarbon, toluene, and ethyl acetate (hereinafter referred to from time to time as “organic solvent-containing air”) is discharged from processes for manufacturing liquid crystals, semiconductors, LEDs, plasma displays, resins, coating materials, and the like, as well as from facilities for printing, coating, cleaning, etc. Since such organic solvents are harmful, the organic solvents in the air discharged from these manufacturing processes, printing equipment, coating equipment, cleaning equipment, and the like must be removed by an appropriate method.
A conventional method for processing an organic solvent-containing air comprises an adsorbing-removing step of removing the organic solvents in the air by causing the air to flow through an adsorbing member, a regenerating step of regenerating the adsorbing member by causing a regeneration air to flow though the adsorbing member which has adsorbed the organic solvents, and a combustion step of feeding a concentrated air produced in the regeneration step to a combustion furnace and burning the organic solvents in the concentrated air. These steps are carried out simultaneously and continuously using an adsorption apparatus equipped with an adsorbing member containing an adsorbent such as zeolite supported thereon and a processing system for an organic solvent-containing air equipped with a combustion furnace packed with an oxidation catalyst.
A conventional method for processing an organic solvent-containing air will be described with reference to FIG. 4. FIG. 4 is a flow chart showing a conventional method for processing an organic solvent-containing air. A conventional processing system 50 for an organic solvent-containing air shown in FIG. 4 has an adsorber 41 equipped with an adsorbing member divided into an adsorption zone and a regenerating zone and a combustion furnace 42 packed with an oxidation catalyst. In the adsorber 41, an air I to be processed is caused to flow through the adsorption zone to adsorb and remove the organic solvents in the air I and, at the same time, the adsorbing member which has adsorbed the organic solvents is regenerated by causing a regeneration air J to flow through the regeneration zone. The regeneration air J used for regenerating the adsorbing member is discharged from the adsorber 41 as a concentrated air containing high-concentration organic solvents. The concentrated air is supplied to the combustion furnace 42 via a concentrated air feed pipe 47. The organic solvents in the concentrated air are burnt in the combustion furnace 42 to remove the organic solvents in the concentrated air and an exhaust gas L is discharged from the combustion furnace 42.
In this manner, in the conventional method of processing an organic solvent-containing air, a processed air K produced by processing the air I to be processed in the adsorber 41 and the exhaust gas L from the combustion furnace are discharged to the atmosphere.
Because the organic solvents burn by being catalyzed with an oxidation catalyst in the combustion furnace, an enormous heat is generated and the oxidation catalyst is exposed to a high temperature. Since a platinum catalyst, of which the upper limit of the operating temperature is 500° C., is commonly used as the oxidation catalyst, if heated above 500° C., the oxidation catalyst decreases its performance due to deterioration by heat. Therefore, it is necessary to control the temperature of the oxidation catalyst in a range not exceeding 500° C. The temperature of the oxidation catalyst is controlled by detecting the temperature of the exhaust gas from the combustion furnace and adjusting the temperature of the air supplied to the combustion furnace according to the temperature of the exhaust gas. The temperature of the air supplied to the combustion furnace is usually in a range of 250° C. to 300° C.
In this conventional method for processing organic solvents, the organic solvents can be burnt only incompletely in the combustion furnace if the concentration of the organic solvents in the air supplied to the combustion furnace is too high. That is, there is an upper limit in the concentration (content) of the organic solvents in the air which can be processed by the combustion furnace.
It is natural that the concentration of the organic solvents in the organic solvent-containing air discharged from the manufacturing processes and the like, namely, the concentration of the organic solvents in the air to be processed, fluctuates. If the concentration of the organic solvents in the air to be processed increases, the concentration of the organic solvents in the air processed in the combustion furnace also increases. When the increase in the concentration of the organic solvents in the air supplied to the combustion furnace is small, the concentration of the organic solvent can be lowered by introducing external air to reduce the concentration to level not exceeding the process limit concentration of the combustion furnace. In regard to the fluctuation of the concentration which may cause trouble in the process, an increase of the concentration is so great that the concentration of the organic solvents must be diluted by introducing a great amount of external air. However, since there is a limitation to the throughput of a combustion furnace, the amount of external air to be introduced is limited. Thus, the problem could not be obviated in some cases by introducing the external air.
In such a case, an organic solvent-containing air exceeding the process limit concentration of the combustion furnace is supplied to the combustion furnace. It is impossible for the combustion furnace alone to completely burn the organic solvent, in which case an unburned organic solvent may mix into the exhaust gas from the combustion furnace. For this reason, an exhaust gas containing an unburned organic solvent may be emitted into the atmosphere from the combustion furnace.
Accordingly, an object of the present invention is to provide a method for processing an organic solvent-containing air which can be operated in spite of a rapid fluctuation of the concentration of the organic solvents in the air to be processed, specifically, a method for processing an organic solvent-containing air which does not increase the organic solvent content in the air to be emitted into the atmosphere after processing, even if the concentration of the organic solvents rapidly changes.